The present invention relates to a mono/stereo input circuit for use in audio equipment, and more particularly, to a circuit for automatically recognizing and receiving mono and stereo audio signals, in which, although a mono connector is inserted into a stereo jack, such an insertion is automatically recognized so that a stereo circuit can operate for mono sound.
FIG. 1 is a circuit diagram of a conventional mono/stereo audio input circuit. In FIG. 1, a microphone connector such as a mono input connector (FIG. 3) or a stereo input connector (FIG. 4) is inserted into a stereo jack 1 having left and right terminals 1L and 1R and a ground terminal. Stereo jack 1 transmits an audio input signal supplied via the inserted microphone connector to a next stage. A mono/stereo selector 2 selects an audio processing circuit included in an amplifier portion 3, by which a mono or stereo audio input signal is transmitted to the proper audio processing circuit according to the type (mono or stereo) of the inserted microphone connector. Amplifier portion 3 amplifies the mono or stereo signal according to a mode selected by selector 2, and outputs the amplified signal to another amplifier stage or a speaker circuit via output terminals 4R and 4L. In FIG. 1, C1 through C7 and R1 through R5 are capacitors and resistors, respectively.
When a mono input is supplied to a circuit configured as above such that a mono connector (FIG. 3) is connected to stereo jack 1, left terminal 1L is connected to a signal portion 15 of the mono connector, which is proper, but right terminal 1R of stereo jack 1 is improperly connected to ground portion 12. As a result, the right input is grounded and only the left input signal is transmitted.
To prevent such a phenomenon and recover the right signal line, the mono/stereo selector 2 is used to disconnect ground portion 12 of the mono connector from amplifier portion 3 and tie the input of the right signal line to that of the left signal line by switching a switching blade SW to the left signal line, so that the mono signal input is fed through both left and right circuits. Thus, the stereo audio apparatus operates as a mono circuit.
In operating the conventional mono/stereo audio input circuit constructed as above, the position of selector 2 must be switched manually to the proper setting, whenever changing from a mono input condition to a stereo input condition, or vice versa, which represents an inconvenience to the user.